Biology For Class X - Chapter No. 7 - Man And His Environment - Short Question Answers

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CHAPTER 7: MAN AND HIS ENVIRONMENT
B. Short Questions Answers

i) What is the effect of light on ecosystem?
Ans: LIGHT:

• Light is the most vital factor, without it life can not exist.
• It is ultimate source of energy for every ecosystem and plays an important role in the lives of both plants and animals.
• Plants convert light energy into chemical energy by the process of photosynthesis. This chemical energy is stored in the form of food which is needed by every living things.
• In terrestrial ecosystems, light is not a limiting factor because only about 3% of available light is used for photosynthesis. However, in deep and turbid waters, light can be a limiting factor for photosynthesis.

Effect Of Light On Organism:
Light affects organisms in three ways:

1. Intensity of light,
2. Its duration or photoperiod and
3. Its quality Or Type (wave length).

1. Intensity of Light:

• The intensity of light depends upon season, latitude, angle of incidence and time of day.
• Intensity of light plays important role in plants.
• In plants intense light may destroy the chlorophyll.
• It also affects opening and closing of the stomata, permeability of the cell membrane, height and surface area of plant etc.
• In animals light affects development of pigments.

2. Exposure time of light (Photoperiod):

• Light is also necessary for vision.
• Duration of light (photoperiod) affects starts of certain biological processes e.g. flowering of certain plants, leaf fall and other aspects of plant growth.
• In animals biological rhythms such as reproductive cycles sleep cycles, hibernation, migration, are affected by light duration.
• Making Vitamin D in human being.

3. Quality of Light:

• Out of seven colours of visible light (electromagnetic spectrum), chlorophyll absorbs only red and blue light for photosynthesis.
• Light of short wave length such as ultraviolet rays is harmful for life.
• Most of the light reaching the earth is converted to heat and thus light also maintains the temperature of the earth and atmosphere in the ecosystem.

ii) Which one is the first trophic level of ecosystem and how?
Ans: TROPHIC LEVELS:
The steps of transfer of energy rich food are called trophic levels.

FIRST TROPHIC LEVEL OF ECOSYSTEM:
PRODUCERS:

• Producers always occupy the first trophic level in any food chain because only producers have the ability to trap solar energy with the help of chlorophyll and synthesis their own food.
• The producers produce food for themselves and other organisms of ecosystem.
• They are primary source of energy for other organisms.
• All members of community depend, directly or indirectly on the producers for their food and energy.
• Producers utilize a part of their food while consumers and decomposers utilize the remaining food.
• Example:
  Green plants and algae are the major producers. They carry out photosynthesis in which they use sunlight for the preparation of food. Some types of photosynthetic bacteria are also producers.

iii) Define nitrogen cycle? What do we mean by nitrogen fixation and how it occurs in an ecosystem?
Ans: NITROGEN CYCLE:
The nitrogen is an essential part of protoplasm, proteins, nucleic acids, chlorophyll etc and is therefore, necessary for living organisms. The exchange of nitrogen between soil and atmosphere and its circulation through bodies of living organisms takes place through inter-related processes known as nitrogen cycle.

This cycle consist of three steps:

1. Nitrogen fixation
2. Nitrification
3. Denitrification

NITROGEN FIXATION:

"Conversion of atmospheric free nitrogen gas into soluble nitrogen compounds (nitrates) is called nitrogen fixation."

Nitrogen Fixation Occurs In Ecosystem:
The atmosphere contains about 78 percent nitrogen gas. It is an inert gas and the organisms cannot use it directly. Therefore, nitrogen is first changed to soluble nitrogen compounds such as nitrates (NO₃) which the plants can absorb from the soil.

Source of Nitrates:
The following are the sources of nitrates for living organisms

1. Nitrogen Fixation by Thunderstorm:
   The atmospheric Nitrogen combines with oxygen during lightning to make certain compound which ultimately form nitrates and reach to soil by rain water.
   
   
2. Nitrogen Fixation by Living Organisms:
   The second source to fix atmospheric Nitrogen are three types of bacteria.
   a) The first group lives in water are called cyanobacteria. They are photosynthetic.
   b) Second group lives in soil.
   c) Third group lives in roots of certain leguminous plants.

These bacteria which help in nitrogen fixation are called nitrogen fixing bacteria.

iv) What is interaction?
Ans: INTERACTION IN ECOSYSTEM:
The organisms in an ecosystem not only interact with their physical environment but also with each other. These interaction maintain balance in growth and population. These interactions may be beneficial or harmful.

Positive Interactions:
In this type of interaction organisms form associations for mutual benefit or for benefit of one species without harming the other.

Negative Interactions:
In this type of interaction one organism gets the benefit and the other is harmed.

Types Of Relationship:
Some of these types of relationships are as follows:
1. Competition:

• This type of a relationship is actually a cold war between the organisms of a community occupying the same habitat.
• The interactions between the organisms lead to close associations between them.
• There are two basic types of associations:
  (a) Intraspecific Association:
  Associations between members of the same species. These associations are found in social animals for social organizations or for formation of social groups. This competition is mainly for food.
  
  (b) Interspecific Associations:
  Associations between different species. In these associations, members of one species feed on members of another species and may also use them as habitat. Intraspecific competition is mainly for mate, better shelter, better and high amount of food. This competition becomes a limiting factor because it ends in the survival of the fittest, and helps to keep the size of population and community in balance.

2. Predation:

• In this relationship one population called predators feeds on the members of another population known as prey.
  Predators: They are larger organisms which capture and kill an alive animal for its food.
  Prey: They are the animals being killed.
• Mostly the predators are secondary or tertiary consumers of an ecosystem.
• The prey-predators interaction keeps the population of both the prey and the predator in equilibrium.
• Any species of a prey without its natural predator, disturbs the balance of the ecosystem due to explosive increase of their population.
• The degree of harm caused by this interaction, depends upon the relative population of the prey and predators.
• Example:
  Predators are usually animals but a few like pitcher plant, venus fly trap etc. are plant predators and are called carnivore plants.

3. Symbiosis:
Generally the symbiosis is defined as an association between two living organisms of different species for mutual benefit or in which one partner gets the benefit and the other is neither benefited nor harmed.
In other words none of the two partners is harmed.

Types Of Symbiosis:
There are three types of symbiosis

1. Parasitism:
   Parasitism is an association between two living organisms in which one lives in or on the body of the other and derives nourishment from it.
   In other words, one gets the benefit and the other is harmed.
   The organism getting the benefit is called the parasite and the one which is harmed is called the host.
   Parasites cause diseases, These disease causing parasites are viruses, bacteria, fungi, protozoa, insects, worms etc.
   A successful parasite takes just enough food from the host to grow and reproduce.
   They have rapid rate of reproduction.
   
   
2. Commensalism:
   It is an association between two living organism of different species in which one is benefited and the other is not affected, that is it is neither benefited nor harmed. The organism getting the benefit is called commensal.
   Example:
   A good example is spirochaetae bacteria that lives between our teeth to obtain food but cause no harm to us.
   
   
3. Mutualism:
   It is an association between two species of living organisms for mutual benefit.
   The two partners are dependent on each other for their survival and growth.
   The organisms in this association may be two animals, two plants or a plant and an animal.
   Example of mutualism:
   are Nitrogen Fixing Bacteria , Rhizobium. They live in the nodules of leguminous plants. The bacteria fix atmospheric nitrogen into nitrates for the plant which is requires for their growth and in return the plant provides shelter and food for the bacteria.

v) What is pyramid of number?
Ans: PYRAMID OF NUMBERS:
The pyramid of numbers was advanced by Charles Elton in 1927. It is define as:

"A pyramid of numbers is a graphical representation of members of population in an area at different in trophic level."

It is an upright pyramid in light of the fact that in an ecosystem, the producers are always more in number than other trophic levels.
For example:

• The grasses sit at the lowest trophic level or the base of the number pyramid because of their abundance.
• The primary consumer, such as a grasshopper, occupies the next higher trophic level. Grasshoppers are fewer in number than grass. The next trophic level is a primary carnivore, such as a rat. There are fewer rats than grasshoppers because they consume grasshoppers.
• Secondary carnivores, such as snakes, occupy the next higher trophic level. Snakes feed on rats and snakes are eaten by hawks, which occupy the highest trophic level and are the least in number.

vi) What is greenhouse effect?
Ans: GREEN HOUSE EFFECT:
Green House Gases:
CO₂ and methane produced during burning of fossil fuels in urban areas are generally called greenhouse gases.

Global Warming OR Green House Effect:
Due to excessive burning of fossil fuels, the amount of CO₂ in atmosphere becomes abnormally high. CO₂ and methane if produced in high quantity in atmosphere are accumulated below the ozone layer, which do not allow heat energy of sun to reflect back in space. As a result, heat remains with in the earth’s atmosphere This phenomenon is called global warming or green house effect.

Effects Of Global Warming:
The possible effects of global warming are:

• Melting of the polar ice and glaciers at high rate.
• which in turn would raise the sea level flooding vast coastal areas.
• Early melting of snows in the mountains would flood large areas of farmland.
• Warming of atmosphere can cause heavy rains and strong hurricanes and storms.

vii) What is algal bloom and how it destroy the life of an aquatic ecosystem?
Ans: EUTROPHICATION OR ALGAL BLOOM:
Growth of algae with very high rate due to increase in phosphorous and nitrogen compounds is called algal bloom or eutrophication.
Agriculture waste, sewage water, factory waste etc run off poses rich quantity of the inorganic nutrients such as phosphorous and nitrogen containing compounds like are detergents. They accumulate in water reservoirs and promote algal growth upto dangerous level i.e. algal bloom.

Effects on Aquatic ecosystem:

• Algal bloom when floats on water surface spoil fishing, swimming and recreational qualities of water.
• As the algae die, the activity of decomposers increase and they consume more and more oxygen. Deficiency of oxygen results in massive death of useful organisms such as fishes.
• The excessive growth of other decomposers also use the excessive oxygen present in water which leads to the death of other organisms.
• It also reduces the light reaching to lower layer of water.

viii) What measure can be taken to control water pollution?
Ans: CONTROL OF WATER POLLUTION:

• Public awareness at all levels is important. It should be through social media, political leaders, institution from pre-primary level.
• Strict legislation and implementation is required on sewage treatment and industrial recycling processes.
• No industrial and agricultural waste should be added to water bodies before complete treatment.

ix) Write down the name of some endangered mammals of Pakistan.
Ans: ENDANGERED MAMMALS OF PAKISTAN:

• Punjab Urial
• Markhor
• Snow Leopard
• Asia snadspit green turtle
• Indus river dolphin
• Bear of Deosai

x) Draw the diagram of nitrogen cycle.

xi) Write down the name of some endangered birds of Pakistan.
Ans: ENDANGERED BIRDS OF PAKISTAN:

• Siberian Crane
• Falcon
• Cheer Pheasant
• Chacor
• Long Billed Vulture
• Red Avadavar

xii) Illustrate acid rain and its effect?
Ans: ACID RAIN:
Acid rain includes any form of precipitation with acidic components, such as sulphuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms. This can include rain, snow, fog, hail or even dust that is acidic.
Due to urbanization and industrialization more fuel burn, more acids are used in industries, as a result of these consumption more CO₂, SO₂, NO₂ are liberated in air from the chimneys. When rain falls through these polluted air H2O react with these gases in air and produce carbonic acid, sulphuric acid and nitric acid.
Effect:
The acid destroy soil, micro-organisms of soil, skin of animals, building material.

xiv) What is meant by depletion of ozone layer?
Ans: Ozone Layer:
In upper atmosphere a protective layer of ozone (O₃) is present which is very important us because it checks the ultraviolet radiations from sun which are lethal for living organisms.

Depletion Of Ozone Layer:
Scientist have found ozone layer is gradually depleting (getting thin) due to chloro flouro carbon (CFC), as they react with ozone and convert it into O₂.
The CFC used as propellant in pressurized aerosol, foaming agent, refrigerators etc. Each one atom of chlorine converts more than 100000 molecules of ozone O₃ to Oxygen O₂.

xv) Draw diagram for sewage treatment?
Ans: SEWAGE TREATMENT: